“Sometimes it’s scary to not know what something is, but it’s also scientifically exciting,” according to the palaeontologist, Corentin Loron, at Edinburgh University. That incongruity lies at the heart of Prototaxites: a trunk-like fossil that at one time stood tall over the first land ecosystems, but yet cannot be squared up with either plants, animals, or fungi.
Prototaxites came into science over 160 years ago in the form of a puzzle that resembled a monument. The biggest ones were about 9 meters (30 feet), which was unlikely in a world that early in the Devonian period had neither forests nor known terrestrial construction. Even in sceneries where the shrubs remained below a meter, this flat, pillar-like form would have been less of terrain than a skyline.
The classification was alluring with that scale. The fossils were theorized by researchers of the nineteenth century as rotting conifer trunks, which is an intuitive deduction of the scholar on the outside. Microscopy made that harder: the inside was constructed of woven tubes, not of blocky cell by cell as the plant tissues. Subsequent hypotheses described Prototaxites as an enormous fungus, or as lichen-like, an association between a fungus and a photosynthetic association. The controversy has prevailed due to the fossil seemingly appearing biological in all aspects that count but not acting like any one of the contemporary groups when subjected to scrutiny.
Especially clean material in the Rhynie chert of Scotland, an ancient hot-spring ecosystem frequently likened to Yellowstone, is the subject of new analyses that show mineral-rich water entraps organisms in stone with such microscopic accuracy. Using this deposit, Loron and others analyzed three fossils and employed such an extraordinary preservation to look for the chemical evidence of original biomolecules. According to Loron, the specimens have been well-preserved to the extent that the chemistry is “not overcooked,” i.e. fossilization has not obliterated important signatures.
The comparison of the decisive kind was one that neighbors in the same rock made. Fungal fossils that were deposited in the same circumstances contain degradation products of the chitin and glucan, structural molecules that assist in the definition of fungal cell walls. Prototaxites did not. Had Prototaxites been fungi, we should have expected it to pursue the same tendency as the fungi since they lie in close proximity to one another in the same burial conditions, Loron said. Formal features were also prominent: scientists have given complex internal branching into the dark spherical areas that may have allowed gaseous, nutrient, or water exchange-like structures, which are the features the study suggests are not shared with any known fungi, living or extinct.
The mystery is neither being closed by independent voices. The work has been described as wonderful analyses by Marc-Andre Selosse of the Natural History Museum in Paris, though he commented that only one species of Prototaxite had been studied out of 25 species of Prototaxites described. That sampling gap allows ecological diversity within the genus, such as lichen-like functionality of certain forms.
According to Kevin Boyce of Stanford University, who proposes that Prototaxites could not use photosynthesis, the idea of comparing previous fossils to the modern mushrooms is misleading because the fossil is too old to be drawn to a one-to-one analogy. Prototaxites would be, in that opinion, one of the first experiments at constructing large bodies on-land- an evolution that those who map evolutionary history might not find reflected in modern kingdoms.
The question of engineering is just as strong as the biological one, how did a tall, tube-built body stand in a young world on earth, how was it anchored? even the simple history of life whether it stood on its heels so long as it existed remains undetermined. The preserved chemistry of Rhynie chert has not, so far, given us a clean label; it has given us, which is even more of a treasure in the field of paleontology, evidence that is sufficiently strong to render uncertainty worthwhile, and sufficiently detailed to focus the next series of inquiries.
